Female pronghorn have been aged at 16 years in the wild, though they seldom live past 9 years. The most common causes of death are predators, hard winters with deep snow, lack of water, and hunting or car collisions. Pronghorns have been recorded living 11 years in captivity.
Average lifespan
Status: wild: 16 years.
Range lifespan
Status: captivity: 11 (high) years.
Average lifespan
Status: wild: 16 years.
Average lifespan
Status: captivity: 11.8 years.
Average lifespan
Status: wild: 10.0 years.
Average lifespan
Status: wild: 10.0 years.
Average lifespan
Status: captivity: 12.0 years.
Pronghorns are primarily found in grassland, sage scrub or chapparal, and desert. The southern portion of their range consists mainly of arid grasslands and open prairies. Throughout the rest of their range they are common in sage scrub and chaparral as well, areas of dense shrubs with tough leaves. Pronghorns are particularly dependent on sage brush for forage in these areas. Pronghorn feed primarily on sage, forbs, and grasses. They have also been known to consume cacti in some areas. There is an overlap in forage preferences with domestic sheep and cattle, so some competition for food occurs. Overgrazing by sheep has been implicated in pronghorn die offs, especially in winter. Pronghorn habitat ranges from sea-level to about 3500 m. Their need for free standing, fresh water varies with the moisture content of the vegetation they consume. They may have to travel a great distance to find a water source. In winter, northern populations depend heavily on sage brush. Pronghorn are commonly found along wind-blown ridges where vegetation has been cleared of snow, although they will dig through snow with their hooves to get to vegetation.
Range elevation: 0 to 3,350 m.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral
Other Habitat Features: suburban ; agricultural
Antilocapra americana is endemic to North America and distributed throughout the treeless plains, basins, and deserts of western North America, from the southern prairie provinces of Canada, southward into the western United States and to northern Mexico. Distribution of populations within this range is discontinuous. In 1959, a population was introduced to Hawaii. However, by 1983 the population was roughly 12 individuals and headed for extinction.
Biogeographic Regions: nearctic (Native )
Pronghorns are herbivores, eating stems, leaves, grasses and shrubs. Pronghorns have been described as "dainty" feeders, feeding on small amounts of a wide variety of plants. Particularly important in their is browse, especially sagebrush in winter. Pronghorns on grasslands have been observed starving in winter, whereas nearby populations in sagebrush survive well. Forbs with high water content are preferred in the summer diet and grasses are generally eaten only when there is new growth. Cacti are also eaten to some extent, especially in southern populations. Pronghorns use foregut fermentation with rumination to break down cellulose. Their stomach is enlarged and compartmentalized into four chambers, as in other ruminants. Water consumption varies with the water content of the vegetation available locally. When tender leaves are available, with moisture content of 75% or more, pronghorns do not seem to need to drink free-standing water. In dry seasons or areas, pronghorns are typically found within 5 to 6 km of water and may drink up to 3 liters per day.
Pronghorns must compete with introduced cattle (Bos taurus) and sheep (Ovis aries) throughout most of their range. In some areas, pronghorn are excluded from areas used by sheep, because the sheep eliminate much of their preferred vegetation. In other areas pronghorn and sheep seem to be able to coexist well. However, pronghorns can do well on areas overgrazed by cattle because they prefer forbs and browse. It is estimated that 1 cow can eat as much as 38 pronghorns. Fences constructed to enclose cattle and sheep can prevent pronghorn movement across rangeland, resulting in starvation and dehydration. Pronghorns can be considered a valuable part of rangeland management because they eat noxious weeds.
Plant Foods: leaves; roots and tubers; wood, bark, or stems
Primary Diet: herbivore (Folivore )
Throughout their range pronghorns co-occur with cattle, bison, sheep, and horses. Pronghorns can improve rangeland quality for these other speces by eating noxious weeds or invasive plants. Introduced livestock may overgraze areas they share with pronghorn, thus reducing cover and quantity of food. The reduction of cover may increase young mortality through predation.
Although there are few epizootic diseases that strongly affect pronghorn populations there are 33 species of roundworms, 21 genera of bacteria, 14 viral diseases, 8 species of protozoa, 5 species of tapeworms, 4 species of ticks, one fluke, and a louse fly that are known to infect them. "Bluetongue" disease has resulted in extensive mortality in some cases. It is an insect-borne viral disease (Bluetongue virus, BTV) that is transmitted by midges (Culicoides imicola). Worm infections have also resulted in extensive fawn mortality in some areas. Pronghorns that co-occur with sheep tend to have higher parasite loads than those in areas without sheep. Pronghorns are the definitive host of a nematode worm that also infects sheep and mule deer: Pseudostertagia bullosa (Nematoda: Trichostrongyloidea). They can also be parasitized by meningeal worms (Parelaphostrongylus tenuis) that are common parasites of white-tailed deer.
Mutualist Species:
Commensal/Parasitic Species:
Pronghorns are an important big games species in the western United States. Their use of open habitat means often hunters have success rates of up to 90 percent.
Positive Impacts: food ; body parts are source of valuable material; research and education
Pronghorns are grazers that will take advantage of wheat or alfalfa fields during the winter if there is deep snow. This may negatively impact crop yield. However, most pronghorn populations occur in areas with little agricultural development.
Negative Impacts: crop pest
It is estimated that up to 35 million pronghorns lived in North America before colonization by western Europeans. By 1924 this number had decreased to less than 20,000. Pronghorn populations have increased since that time and are now considered the second most numerous game species in North America.
The IUCN Red List lists Antilocapra americana as lower risk/least concern. Populations are stable, widespread, and relatively common throughout most of their range, with an estimated population size of 0.5 to 1 million. The U.S. Endangered Species Act recognizes two populations as endangered: Sonora pronghorns (A. a. sonoriensis) and peninsular pronghorns (A. a. peninsularis). Populations of Sonoran pronghorn in Mexico have been protected since 1967 and have undergone several recovery plans, the most recent in 1998. This population of pronghorn is listed under the Convention of International Trade of Endangered Flora and Fauna (CITES) Appendix I.
US Federal List: endangered
CITES: appendix i
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Doe-fawn recognition seems to be through a combination of visual, vocal, and olfactory cues. Scent glands are widely used in male-male and male-female behavioral interactions. Scent glands are used to mark territories, attract potential mates, identify a mate, alert danger, or deter other males intruding in their territory. Both sexes have rump glands and interdigital glands; males also have a gland below each ear and on the back.
Communication Channels: visual ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
Common names for Antilocapra americana include pronghorn, pronghorn antelope, and berrendo (Spanish). Antilocapra americana has also been known by the synonyms Antilope americanus, Antilope (Dicranocerus) furcifer, and Antilocapra anteflexa. There are currently five subspecies recognized: American pronghorns (A. a. americana Ord), Oregon pronghorns (A. a. oregona Bailey), Mexican pronghorns(A. a. mexicana Merrian), peninsula pronghorns (A. a. peninsularis Nelson), and Sonoran pronghorns (A. a. sonoriensis Goldman).
The fossil record dates to the Miocene. Antilocapra americana is the only extant species of a group that was once much more diverse, with 13 extinct genera of antilocaprines known from the Pliocene throughout the current range of A. americana.
Pronghorns are small ungulates with barrel-shaped bodies. Females stand 860 mm at the shoulder and males 875 mm at the should. Females are approximately 1406 mm in body length and males are approximately 1415 mm. The tail is up to 105 mm long and ears are up to 143 mm long. Their body weight is from 35 to 70 kg, depending on sex and age. Their hair is dense and very coarse and is air-filled, providing excellent insulation. Guard hairs are hollow and underlain by finer, shorter underfur. Guard hairs are erectile for heat regulation. As more air becomes trapped in fur, the more they are insulated from external temperatures. Their dorsal fur is a rufous brown and they have creamy underbellies, rumps, and neck patches. Males have short black manes on the neck, from 70 to 100 mm in length, as well as a neck patch and a black stripe that runs across the forehead from horn to horn. Females lack these black facial patches, but have a small mass of black hair around their nose. Their ears are small and point slightly inward at the tip. Pronghorns have a patch of white, erectile fur on their rumps that is visible at great distances. The mucous membranes and eyelashes are coal black. Southern populations are paler in overall color than northern populations. The horns are erect, with a posterior hook and a short anterior prong. The prong gives rise to the common name “pronghorn”. This pronged pattern is unique to this species. The horn is a keratinized sheath, black in color, and is deciduous. Horn sheaths grow over a bony extension of the frontal bone, which is now called the cancellous bone in ungulates. A new sheath forms under the old, which splits and is dropped just after the rut each year. Both sexes have horns, although the horns of females are generally small or absent, and never exceed ear length. Female horns average about 120 mm and the prongs are not prominent. The horn begins to grow at the age of six months and will be shed by 18 months. The maximum horn height for males will occur within 2 to 3 years of age and will average 250 mm, exceeding the length of the ear.
Pronghorn limbs are specialized for cursoriality, giving them enhanced speed and endurance. They are the fastest known New World mammal, traveling at speeds of 98 km/h when sprinting, and can hold a sustained speed of 59 to 65 km/h. The advantages to having speed and endurance include the ability to forage over large areas, to seek new food sources when familiar sources fail, and the ability to escape predators. Pronghorns have unguligrade foot posture, which lengthens the legs by allowing them to stand on the tips of their digits. The length of the radius bone is as long, or longer, than the femur. The ulna is reduced and partially fused to the radius. The clavicle in ungulates has been lost and the scapula has been reoriented to lie flat against the side of their chest where it is free to rotate roughly 20° to 25° in the same plane in which the leg swings. The ulna and radius have been reduced to eliminate the twisting and rotating of the elbow. The reduction of bone and associated muscles in the distal limbs decreases limb weight, giving them more speed. Pronghorns have modified their joints to act as hinges allowing only motion in the line of travel. This has been done by introducing interlocking spines and grooves in their joints. All these adaptations have made pronghorns excel in cursorial locomotion, but they can no longer jump because they have lost the suspension mechanism that cervids have. This explains their apparent fear of fences.
The dental formula of Antilocapra americana is 0/3-0/1-3/3-3/3, where incisors and canines only occur on the lower jaw. Pronghorns have hypsodont crown height; discernable roots do not occur, allowing the cheek teeth to be ever growing. An approximate age when the molars erupt varies slightly; the first comes in at 2 months and the second and third come in around 15 months of age. Replacement of incisors varies as the first is replaced at 15 months, the second at 27, and the third at 39 months. Canines are replaced between 39 and 41 months. Premolars are all replaced at 27 months of age. The sequence of tooth eruption, replacement, and wear is used to estimate the age of pronghorns. Cementum annuli analysis of the first permanent incisor is used for older age classes.
Maximal rate of oxygen intake in pronghorns determines the peak at which the animal can synthesize ATP by aerobic catabolism. This then determines how intensely the animal can exercise. Pronghorns are an extreme example of evolutionary specialization for high oxygen consumption. When comparing body weight to weight-specific consumption of oxygen, pronghorns have values three times higher than the that expected for their body size. This high oxygen consumption makes pronghorns Earth’s fastest sustained runner. Unlike cheetahs, also one of the fastest animals on Earth, pronghorns produce ATP required to run fast aerobically. They have exceptionally large lungs for their body size and exceptional abilities to maintain high rates of blood circulation.
Range mass: 47 to 70 kg.
Average mass: 50-57 kg.
Range length: 1.75 (high) m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; male more colorful; ornamentation
Average basal metabolic rate: 50.973 W.
Fawns or weaker pronghorns are preyed on by coyotes, bobcats, wolves, mountain lions, golden eagles, and other predators within their range. Pronghorns can use their horns to help defend themselves, but they primarily use their speed to escape predators. They are capable of sprints up to 86 km per hour and sustained speeds of 59 to 65 km/hr, making them one of the fastest land mammals. Pronghorns also use their feet in fighting off predators. They have keen eyesight and can spot an object from approximately two miles away. Pronghorns are curious animals and will move towards an intruder until they can detect what it is. If they determine that it is a threat, they will flee. When disturbed, pronghorns erect the white fur on their rumps, which acts to warn others of a disturbance.
Known Predators:
Anti-predator Adaptations: cryptic
Pronghorns are polygynous. Males defend territories from March through the end of the rut in early October. They defend a small harem of females in their territories during that time. Males with territories that contain a water source and have topographic features that help them corner does, do better than males without those features in their territories. Depending on a female's body condition, she will search among territorial males for potential mates. This behavior may last for two to three weeks. Pronghorns have scent glands that emit pheromones to attract or identify mates. These pheromones are important to interactions between sexes. Scent glands are located on either side of the jaw, between the hooves, on the rump, and above the tail. The glands on the neck are larger in males and are thought to be associated with sexual interaction as they are more active during the rutting season. Before mating, a male will approach a female from behind and shake his head to emit pheromones to attract the female. Males also use scent gland secretions to mark tall grasses on territorial boundaries. Males also mark territories with scrapes where they urinate and defecate, using a stereotypes "sniff, paw, urinate, defecate" sequence that may be repeated. Male interactions can include some or all of the following: 1) staring, 2) vocalization by the territory holder (a decrescendo snort-wheeze), 3) approaching an intruder, which can be accompanied by head thrashing, sneezes, and teeth grinding, 4) interacting with an intruder, and 5) chasing, which can be for only a few meters or up to 5 km. Male use of the snort-wheeze vocalization is often accompanied by erection of the mane, rump patches, and the cheek patches. If an intruder does not run away, then the two males walk in parallel to each other in a slow, deliberate manner with their heads held low. If a fight occurs, the males thrust their horns at each other in an attempt to do injury. Males end up in horn-horn or head-head pushing battles in which they try to knock the other off balance. Fights average only about 2 minutes long, but often result in serious injury.
Mating System: polygynous
Breeding occurs from mid-September to October in northern parts of the pronghorn range and from July to October in southern parts of their range. Females ovulate from 4 to 7 ova at the time of mating. These ova quickly travel to the uterus and form blastocysts, where they absorb nutrition for almost a month before implantation. Blastocysts develop long, thread-like walls that begin to twist together and form knots. One quarter to one third of blastocysts die of malnutrition when this knotting reduces the membrane surface area. As many as 7 embryos may still survive this knotted blastocyst stage. However, as the embryos develop, distal embryos are forced into the oviduct, where they perish from lack of nutrition and are reabsorbed. The gestation period is about 252 days and births are synchronous, with all females giving birth within a few days of each other. Females give birth to one or two fawns in the spring, typically they have a single young in their first year of breeding and twins in subsequent years. Females often labor on their sides, but stand as the front legs of the fawn begin to emerge from the vulva. Females and their young form bands in the summer that roam over the territories of one to several males. Pronghorns have 4 inguinal mammary glands. Young are partially weaned by 3 weeks old, at which point they begin to eat vegetation as well. Most female pronghorns breed in their second year, at about 16 months old, although some females can breed as early as 5 months old. Males can breed in their first year, but rarely do because older, dominant males monopolize breeding opportunities. Males typically begin to breed in their third year.
Breeding interval: Pronghorns breed once yearly.
Breeding season: onghorn range and from July to October in southern parts of their range.
Range number of offspring: 1 to 2.
Average gestation period: 252 days.
Average weaning age: 3 weeks.
Range time to independence: 1 to 1.5 years.
Range age at sexual or reproductive maturity (female): 5 (low) months.
Average age at sexual or reproductive maturity (female): 16 months.
Range age at sexual or reproductive maturity (male): 1 to 3 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average birth mass: 3000 g.
Average gestation period: 235 days.
Average number of offspring: 2.
Female pronghorns care for their young from 1 to 1.5 years after birth, after which the young will become independent. At the time of birth, the mother will consume the afterbirth to prevent detection by predators. She also consumes any excrement of the young for the first few weeks of their life to prevent detection by predators. For several days after birth young are weak and unable to keep the pace with adults, so mothers and young rest near a source of water until they gain their strength. Females leave their young in a hidden location in vegetation while they forage, but remain within two miles of them. Within minutes after birth, young pronghorns can stand on their own and they nurse within 2 hours. Within days of birth, young pronghorns can outrun a human and begin to travel and forage with their mother and other females and young in summer bands. Siblings are generally on their own until they begin to travel with their mother. Fawns play extensively in the summer herds, developing strength and dexterity. Male pronghorns do not help in raising offspring.
Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female)
One of nature’s most amazing migrations is that of the pronghorn antelope. Pronghorn have the second longest land mammal migration in North America, a trek of roughly 150 miles coming in second to the caribou which treks over 3000 miles a year (Kostyal, 2011). Given this elite status, it may be somewhat surprising that pronghorn are considered partially migratory; although some individuals migrate long distances seasonally, others only move a few miles a year (White et al., 2007). The Teton herd, known for their extreme migration, travel from their summer foraging grounds in Grand Teton National Park to their wintering grounds in the Green River Basin, south of Pinedale, Wyoming, ins a three to four day, 150-mile trek (Kostyal, 2011). This path is one of only two long-distance migration routes remaining in the Greater Yellowstone region. The other route, located in Idaho, is a much smaller trek of only 80 miles (Cohn, 2010). No matter how short of a journey, both of these herds face many obstacles along the way. The first threat is weather—which is the main reason for these migrations. The weather is a serious threat due to the fact that once snow hits the ground pronghorn antelope lose their biggest advantage: speed. This affects their survival by making them vulnerable to predators, such as wolves (Kostyal, 2011). In addition, deep snow prevents pronghorn from being able to reach their food. If they do not leave the Grand Teton National Park during winter they have high chance of dying due to starvation, predation, hypothermia, or exhaustion, due to difficulties of movement through the deep snow (Cohn, 2010). Another threat to pronghorn is barb wire fences blocking the migration routes. This is a serious issue since pronghorn antelope are not built for jumping. As a result, pronghorn will typically try to go under the fence, causing severe wounds and sometimes deaths due to entanglement (Kostyal, 2011). The most challenging obstacles are highways and interstates. Biologists will even direct traffic to allow them to migrate safely across the roads (Cohn, 2010). Upon arriving in the Green River Basin, the Teton herd spends their winter foraging on the foliage under the snow. As the snow begins to melt in the spring, the migration back to the Grand Teton National Park is a more drawn out journey which happens over roughly two months (Kostyal, 2011). This allows the pronghorn to slowly regain the strength that winter has drained from them. As they become stronger the obstacles become less life-threatening, which allows them to survive the journey back to the Greater Yellowstone area, only to repeat the process the following fall.
Although this is example showcases some of the hazards on long pronghorn migrations, most pronghorn populations do not migrate (Jacques et al., 2009). Over their winter and summer they only move short distances, as small as 13 miles a year (Jacques et al., 2009). The pronghorn that do make extreme migrations such as the Teton herd do so because of the extreme winter weather that occurs in their summer range (Kostyal, 2011). Pronghorn antelope in other regions are not challenged by the severe winter snow that the Teton herd faces, therefore there is no reason for them to move more than a few miles a year for foraging (Jacques et al., 2009).
This taxon is found in the California Central Valley grasslands, which extend approximately 430 miles in central California, paralleling the Sierra Nevada Range to the east and the coastal ranges to the west (averaging 75 miles in longitudinal extent), and stopping abruptly at the Tehachapi Range in the south. Two rivers flow from opposite ends and join around the middle of the valley to form the extensive Sacramento-San Joaquin Delta that flows into San Francisco Bay.
Perennial grasses that were adapted to cool-season growth once dominated the ecoregion. The deep-rooted Purple Needle Grass (Nassella pulchra) was particularly important, although Nodding Needle Grass (Stipa cernua), Wild Ryes (Elymus spp.), Lassen County Bluegrass (Poa limosa), Aristida spp., Crested Hair-grass (Koeleria pyramidata), Deergrass (Muhlenbergia rigens,), and Coast Range Melicgrass (Melica imperfecta) occurred in varying proportions. Most grass growth occurred in the late spring after winter rains and the onset of warmer and sunnier days. Interspersed among the bunchgrasses were a rich array of annual and perennial grasses and forbs, the latter creating extraordinary flowering displays during certain years. Some extensive mass flowerings of the California Poppy (Eschscholzia californica), Lupines (Lupinus spp.), and Exserted Indian Paintbrush (Castilleja exserta) are found in this grassland ecoregion.
Prehistoric grasslands here supported several herbivores including Pronghorn Antelope (Antilocapra americana), elk (including a valley subspecies, the Tule Elk, (Cervus elaphus nannodes), Mule Deer (Odocoileus hemionus), California ground squirrels, gophers, mice, hare, rabbits, and kangaroo rats. Several rodents are endemics or near-endemics to southern valley habitats including the Fresno Kangaroo Rat (Dipodomys nitratoides exilis), Tipton Kangaroo Rat (Dipodomys nitratoides nitratoides), San Joaquin Pocket Mouse (Perognathus inornatus), and Giant Kangaroo Rat (Dipodomys ingens). Predators originally included grizzly bear, gray wolf, coyote, mountain lion, ringtail, bobcat, and the San Joaquin Valley Kit Fox (Vulpes velox), a near-endemic.
The valley and associated delta once supported enormous populations of wintering waterfowl in extensive freshwater marshes. Riparian woodlands acted as important migratory pathways and breeding areas for many neotropical migratory birds. Three species of bird are largely endemic to the Central Valley, surrounding foothills, and portions of the southern coast ranges, namely, the Yellow-billed Magpie (Pica nuttalli), the Tri-colored Blackbird (Agelaius tricolor EN), and Nuttall’s Woodpecker (Picoides nuttallii).
The valley contains a number of reptile species including several endemic or near-endemic species or subspecies such as the San Joaquin Coachwhip (Masticophis flagellum ruddocki), the Blunt-nosed Leopard Lizard (Gambelia sila EN), Gilbert’s Skink (Plestiodon gilberti) and the Sierra Garter Snake (Thamnophis couchii). Lizards present in the ecoregion include: Coast Horned Lizard (Phrynosoma coronatum NT); Western Fence Lizard (Sceloporus occidentalis); Southern Alligator Lizard (Elgaria multicarinata); and the Northern Alligator Lizard (Elgaria coerulea).
There are only a few amphibian species present in the California Central Valley grasslands ecoregion. Special status anuran taxa found here are: Foothill Yellow-legged Frog (Rana boylii NT); Pacific Chorus Frog (Pseudacris regilla); and Western Spadefoot Toad (Pelobates cultripes). The Tiger Salamander (Ambystoma tigrinum) occurs within this ecoregion.
Although many endemic plant species are recognized, especially those associated with vernal pools, e.g. Prickly Spiralgrass (Tuctoria mucronata). A number of invertebrates are known to be restricted to California Central Valley habitats. These include the Delta Green Ground Beetle (Elaphrus viridis CR) known only from a single vernal pool site, and the Valley Elderberry Longhorn Beetle (Desmocerus californicus dimorphus) found only in riparian woodlands of three California counties.
Vernal pool communities occur throughout the Central Valley in seasonally flooded depressions. Several types are recognized including valley pools in basin areas which are typically alkaline or saline, terrace pools on ancient flood terraces of higher ground, and pools on volcanic soils. Vernal pool vegetation is ancient and unique with many habitat and local endemic species. During wet springs, the rims of the pools are encircled by flowers that change in composition as the water recedes. Several aquatic invertebrates are restricted to these unique habitats including a species of fairy shrimp and tadpole shrimp.
This taxon is found in the Chihuahuan Desert, which is one of the most biologically diverse arid regions on Earth. This ecoregion extends from within the United States south into Mexico. This desert is sheltered from the influence of other arid regions such as the Sonoran Desert by the large mountain ranges of the Sierra Madres. This isolation has allowed the evolution of many endemic species; most notable is the high number of endemic plants; in fact, there are a total of 653 vertebrate taxa recorded in the Chihuahuan Desert.Moreover, this ecoregion also sustains some of the last extant populations of Mexican Prairie Dog, wild American Bison and Pronghorn Antelope.
The dominant plant species throughout the Chihuahuan Desert is Creosote Bush (Larrea tridentata). Depending on diverse factors such as type of soil, altitude, and degree of slope, L. tridentata can occur in association with other species. More generally, an association between L. tridentata, American Tarbush (Flourensia cernua) and Viscid Acacia (Acacia neovernicosa) dominates the northernmost portion of the Chihuahuan Desert. The meridional portion is abundant in Yucca and Opuntia, and the southernmost portion is inhabited by Mexican Fire-barrel Cactus (Ferocactus pilosus) and Mojave Mound Cactus (Echinocereus polyacanthus). Herbaceous elements such as Gypsum Grama (Chondrosum ramosa), Blue Grama (Bouteloua gracilis) and Hairy Grama (Chondrosum hirsuta), among others, become dominant near the Sierra Madre Occidental. In western Coahuila State, Lecheguilla Agave (Agave lechuguilla), Honey Mesquite (Prosopis glandulosa), Purple Prickly-pear (Opuntia macrocentra) and Rainbow Cactus (Echinocereus pectinatus) are the dominant vascular plants.
Because of its recent origin, few warm-blooded vertebrates are restricted to the Chihuahuan Desert scrub. However, the Chihuahuan Desert supports a large number of wide-ranging mammals, such as the Pronghorn Antelope (Antilocapra americana), Robust Cottontail (Sylvilagus robustus EN); Mule Deer (Odocoileus hemionus), Grey Fox (Unocyon cineroargentinus), Jaguar (Panthera onca), Collared Peccary or Javelina (Pecari tajacu), Desert Cottontail (Sylvilagus auduboni), Black-tailed Jackrabbit (Lepus californicus), Kangaroo Rats (Dipodomys sp.), pocket mice (Perognathus spp.), Woodrats (Neotoma spp.) and Deer Mice (Peromyscus spp). With only 24 individuals recorded in the state of Chihuahua Antilocapra americana is one of the most highly endangered taxa that inhabits this desert. The ecoregion also contains a small wild population of the highly endangered American Bison (Bison bison) and scattered populations of the highly endangered Mexican Prairie Dog (Cynomys mexicanus), as well as the Black-tailed Prairie Dog (Cynomys ludovicianus).
The Chihuahuan Desert herpetofauna typifies this ecoregion.Several lizard species are centered in the Chihuahuan Desert, and include the Texas Horned Lizard (Phrynosoma cornutum); Texas Banded Gecko (Coleonyx brevis), often found under rocks in limestone foothills; Reticulate Gecko (C. reticulatus); Greater Earless Lizard (Cophosaurus texanus); several species of spiny lizards (Scelopoprus spp.); and the Western Marbled Whiptail (Cnemidophorus tigris marmoratus). Two other whiptails, the New Mexico Whiptail (C. neomexicanus) and the Common Checkered Whiptail (C. tesselatus) occur as all-female parthenogenic clone populations in select disturbed habitats.
Representative snakes include the Trans-Pecos Rat Snake (Bogertophis subocularis), Texas Blackhead Snake (Tantilla atriceps), and Sr (Masticophis taeniatus) and Neotropical Whipsnake (M. flagellum lineatus). Endemic turtles include the Bolsón Tortoise (Gopherus flavomarginatus), Coahuilan Box Turtle (Terrapene coahuila) and several species of softshell turtles. Some reptiles and amphibians restricted to the Madrean sky island habitats include the Ridgenose Rattlesnake (Crotalus willardi), Twin-spotted Rattlesnake (C. pricei), Northern Cat-eyed Snake (Leptodeira septentrionalis), Yarrow’s Spiny Lizard (Sceloporus jarrovii), and Canyon Spotted Whiptail (Cnemidophorus burti).
There are thirty anuran species occurring in the Chihuahuan Desert: Chiricahua Leopard Frog (Rana chircahuaensis); Red Spotted Toad (Anaxyrus punctatus); American Bullfrog (Lithobates catesbeianus); Canyon Treefrog (Hyla arenicolor); Northern Cricket Frog (Acris crepitans); Rio Grande Chirping Frog (Eleutherodactylus cystignathoides); Cliff Chirping Frog (Eleutherodactylus marnockii); Spotted Chirping Frog (Eleutherodactylus guttilatus); Tarahumara Barking Frog (Craugastor tarahumaraensis); Mexican Treefrog (Smilisca baudinii); Madrean Treefrog (Hyla eximia); Montezuma Leopard Frog (Lithobates montezumae); Brown's Leopard Frog (Lithobates brownorum); Yavapai Leopard Frog (Lithobates yavapaiensis); Western Barking Frog (Craugastor augusti); Mexican Cascade Frog (Lithobates pustulosus); Lowland Burrowing Frog (Smilisca fodiens); New Mexico Spadefoot (Spea multiplicata); Plains Spadefoot (Spea bombifrons); Pine Toad (Incilius occidentalis); Woodhouse's Toad (Anaxyrus woodhousii); Couch's Spadefoot Toad (Scaphiopus couchii); Plateau Toad (Anaxyrus compactilis); Texas Toad (Anaxyrus speciosus); Dwarf Toad (Incilius canaliferus); Great Plains Narrowmouth Toad (Gastrophryne olivacea); Great Plains Toad (Anaxyrus cognatus); Eastern Green Toad (Anaxyrus debilis); Gulf Coast Toad (Incilius valliceps); and Longfoot Chirping Toad (Eleutherodactylus longipes VU). The sole salamander occurring in the Chihuahuan Desert is the Tiger Salamander (Ambystoma tigrinum).
Common bird species include the Greater Roadrunner (Geococcyx californianus), Burrowing Owl (Athene cunicularia), Merlin (Falco columbarius), Red-tailed Hawk (Buteo jamaicensis), and the rare Zone-tailed Hawk (Buteo albonotatus). Geococcyx californianus), Curve-billed Thrasher (Toxostoma curvirostra), Scaled Quail (Callipepla squamata), Scott’s Oriole (Icterus parisorum), Black-throated Sparrow (Amphispiza bilineata), Phainopepla (Phainopepla nitens), Worthen’s Sparrow (Spizella wortheni), and Cactus Wren (Campylorhynchus brunneicapillus). In addition, numerous raptors inhabit the Chihuahuan Desert and include the Great Horned Owl (Bubo virginianus) and the Elf Owl (Micrathene whitneyi).
The pronghorn (UK: /ˈprɒŋhɔːrn/, US: /ˈprɔːŋ-/)[4] (Antilocapra americana) is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American antelope, prong buck, pronghorn antelope and prairie antelope,[5] because it closely resembles the antelopes of the Old World and fills a similar ecological niche due to parallel evolution.[6] It is the only surviving member of the family Antilocapridae.[7]
During the Pleistocene epoch, about 11 other antilocaprid species existed in North America.[8] Three other genera (Capromeryx,[9][10] Stockoceros[11][12] and Tetrameryx[13]) existed when humans entered North America but are now extinct.
As a member of the superfamily Giraffoidea, the pronghorn's closest living relatives are the giraffe and okapi.[14] The Giraffoidea are in turn members of the infraorder Pecora, making pronghorns more distant relatives of the Cervidae (deer) and Bovidae (cattle, goats, sheep, antelopes, and gazelles), among others.
The pronghorn is the fastest land mammal in the Western Hemisphere, with running speeds of up to 88.5 km/h (55 mph). It is the symbol of the American Society of Mammalogists.[15]
Prior to the arrival of the Europeans, the pronghorn was particularly abundant in the region of the Plains Indians and the region of the indigenous people of the Northwest Plateau and was hunted as a principal food source by the local tribes.[16] The pronghorn has also featured prominently in Native American mythology and oral history.[17]
The scientific name of the pronghorn is Antilocapra americana. Although first seen and described by Spanish explorers in the 16th century, the species was not formally recorded or scrutinized until the expedition in 1804-06 by Captain Meriwether Lewis and Second Lieutenant William Clark.[18] Following the discovery of a few subspecies of the sharp-tailed grouse, Lewis and Clark came across the pronghorn near the mouth of the Niobrara River, in present-day Nebraska. Clark was among the first Euro-Americans to publish the experience of killing a pronghorn, and described his experience as follows:[19]
I walked on shore to find an old Vulcanoe [the Ionia Volcano?] ... in my walk I killed a Buck Goat of this Countrey, about the height of the Grown Deer, its body Shorter the horns which is not very hard and forks 2⁄3 up one prong Short the other round & Sharp arched, and is immediately above its Eyes the Color is a light gray with black behind its ears down the neck, and its face white round its neck, its Sides and its rump round its tail which is Short & white; Verry actively made, has only a pair of hoofs to each foot, his brains on the back of his head, his Nostrals large, his eyes like a Sheep he is more like the Antilope or Gazelle of Africa than any other Species of Goat.
Lewis and Clark made several other observations on the behavior of the pronghorn and how the local tribes hunted them. They described the animal, which they referred to as the "Antelope" or the "Goat", as follows:[20]
Of all the animals we have seen the Antelope seems to possess the most wonderful fleetness. Shy and timorous they generally repose only on the ridges, which command a view of all the approaches of an enemy ... When they first see the hunters they run with great velocity ... The Indians near the Rocky Mountains hunt these animals on horseback, and shoot them with arrows. The Mandans' mode of hunting them is to form a large, strong pen or fold, from which a fence made of bushes gradually widens on each side. The animals are surrounded by the hunters, and gently driven towards this pen, in which they imperceptibly find themselves enclosed, and are then at the mercy of the hunters.
The pronghorn was first officially described by American ornithologist George Ord in 1815.[20]
Pronghorns have distinct white fur on their rumps, sides, breasts, bellies, and across their throats. Adult males are 1.3–1.5 m (4 ft 3 in – 4 ft 11 in) long from nose to tail, stand 81–104 cm (2 ft 8 in – 3 ft 5 in) high at the shoulder, and weigh 40–65 kg (88–143 lb). The females are the same height as males, but weigh 34–48 kg (75–106 lb). The feet have two hooves, with no dewclaws. Their body temperature is 38 °C (100 °F).[8][21][22][23]
The orbits (eye sockets) are prominent and set high on the skull. Their teeth are hypsodont, and their dental formula is 0.0.3.33.1.3.3.
Each horn of the pronghorn is composed of a slender, laterally flattened blade of bone which is thought to grow from the frontal bones of the skull, or from the subcutaneous tissues of the scalp, forming a permanent core.[24] As in the Giraffidae, skin covers the bony cores, but in the pronghorn, it develops into a keratinous sheath which is shed and regrown annually. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath having a forward-pointing tine (hence the name pronghorn). Males have a horn sheath about 12.5–43 cm (5–17 in) (average 25 cm or 10 in) long with a prong. Females have smaller horns that range from 3–15 cm (1–6 in) (average 12 cm or 4+1⁄2 in) and sometimes barely visible; they are straight and very rarely pronged.[22] Males are further differentiated from females in having a small patch of black hair at the angle of the mandible. Pronghorns have a distinct, musky odor. Males mark territory with a preorbital scent gland which is on the sides of the head.[8] They also have very large eyes with a 320° field of vision. Unlike deer, pronghorns possess a gallbladder.[25]
The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximum predator evasion through running. The top speed is dependent upon the length of time over which it is measured. It can run 56 km/h (35 mph) for 6.5 km (4 mi), 68 km/h (42 mph) for 1.5 km (1 mi), and 88.5 km/h (55 mph) for 800 m (1⁄2 mi).[21][26] Although it is slower than the African cheetah,[27] it can sustain top speeds much longer than cheetahs.[7] The pronghorn may have evolved its running ability to escape from now-extinct predators such as the American cheetah, since its speed greatly exceeds that of all extant North American predators.[7][28]: 318 Compared to its body size, the pronghorn has a large windpipe, heart, and lungs to allow it to take in large amounts of air when running. Additionally, pronghorn hooves have two long, cushioned, pointed toes which help absorb shock when running at high speeds.[29] They also have an extremely light bone structure and hollow hair.
Pronghorns are built for speed, not for jumping. Since their ranges are sometimes affected by sheep ranchers' fences, they can be seen going under fences, sometimes at high speed. For this reason, the Arizona Antelope Foundation and others are in the process of removing the bottom barbed wire from the fences, and/or installing a barbless bottom wire.[30]
The pronghorn has been observed to have at least 13 distinct gaits, including one reaching nearly 7.3 m (23 ft 11 in) per stride.[7]
The present-day range of the pronghorn extends from southern Saskatchewan and Alberta in Canada south into the United States through Montana, Idaho, Utah, Nevada, Arizona, Nebraska, Wyoming, Colorado, New Mexico, Washington, and central Texas west to coastal southern California[31][32] and northern Baja California Sur, to Sonora and San Luis Potosí in northern Mexico.[8][33] They have been extirpated from Iowa and Minnesota in the United States and from Manitoba in Canada.[34]
A subspecies known as the Sonoran pronghorn (A. a. sonoriensis) occurs in Arizona and Mexico.[22] Other subspecies include the Mexican pronghorn (A. a. mexicana), the Oregon pronghorn (A. a. oregona), and the critically endangered Baja California pronghorn (A. a. peninsularis).
Pronghorns prefer open, expansive terrain at elevations varying between 900 and 1,800 m (3,000 and 5,900 ft), with the densest populations in areas receiving around 250–400 mm (10–15+1⁄2 in) of rainfall per year. They eat a wide variety of plant foods, often including plants unpalatable or toxic to domestic livestock, though they also compete with them for food.[21] In one study, forbs comprised 62% of their diet, shrubs 23%, and grasses 15%,[21] while in another, cacti comprised 40%, grass 22%, forbs 20%, and shrubs 18%.[22] Pronghorns also chew and eat (ruminate) cud.
Healthy pronghorn populations tend to stay within 5.0–6.5 km (3–4 mi) of a water source.
An ongoing study by the Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society shows an overland migration route that covers more than 260 km (160 mi).[35] The migrating pronghorn start travel from the foothills of the Pioneer Mountains through Craters of the Moon National Monument to the Continental Divide. Dr. Scott Bergen of the Wildlife Conservation Society says "This study shows that pronghorn are the true marathoners of the American West. With these new findings, we can confirm that Idaho supports a major overland mammal migration - an increasingly rare phenomenon in the U.S. and worldwide."[36]
Cougars (Puma concolor), wolves (Canis lupus), coyotes (Canis latrans), grizzly bears (Ursus arctos horribilis) and bobcats (Lynx rufus) are major predators of pronghorns. Golden eagles (Aquila chrysaetos) have been reported to prey on fawns and adults. Jaguars (Panthera onca) also likely prey on pronghorns in their native range in the southwestern United States and in northern Mexico.
Pronghorns form mixed-sex herds in the winter. In early spring, the herds break up, with young males forming bachelor groups, females forming harems, and adult males living solitarily.[28] Some female bands share the same summer range, and bachelor male bands form between spring and fall. Females form dominance hierarchies with few circular relationships.[37] Dominant females aggressively displace other females from feeding sites.
Adult males either defend a fixed territory that females may enter, or defend a harem of females. A pronghorn may change mating strategies depending on environmental or demographic conditions.[28]: 228 Where precipitation is high, adult males tend to be territorial and maintain their territories with scent marking, vocalizing, and challenging intruders.[38] In these systems, territorial males have access to better resources than bachelor males.[38] Females also employ different mating strategies. "Sampling" females visit several males and remain with each for a short time before switching to the next male at an increasing rate as estrous approaches. "Inciting" females behave as samplers until estrous, and then incite conflicts between males, watching and then mating with the winners.[39] Before fighting, males try to intimidate each other. If intimidation fails, they lock horns and try to injure each other.[22] "Quiet" females remain with a single male in an isolated area throughout estrous.[39] Females continue this mating behavior for two to three weeks.[22]
When courting an estrous female, a male pronghorn approaches her while softly vocalizing[40][28] and waving his head side to side, displaying his cheek patches.[41] The scent glands on the pronghorn are on either side of the jaw, between the hooves, and on the rump.[22] A receptive female remains motionless, sniffs his scent gland, and then allows the male to mount her.[28]
Pronghorns have a gestation period of 7–8 months, which is longer than is typical for North American ungulates. They breed in mid-September, and the doe carries her fawn until late May. The gestation period is around six weeks longer than that of the white-tailed deer. Females usually bear within a few days of each other.[21] Twin fawns are common.[29] Newborn pronghorns weigh 2–4 kg (4–9 lb), most commonly 3 kg (7 lb). In their first 21–26 days, fawns spend time hiding in vegetation.[38] Fawns interact with their mothers for 20–25 minutes a day; this continues even when the fawn joins a nursery.[38] The females nurse, groom, and lead their young to food and water, as well as keep predators away from them.[38] Females usually nurse the young about three times a day.[21] Males are weaned 2–3 weeks earlier than females.[38] Sexual maturity is reached at 15 to 16 months, though males rarely breed until three years old. Their lifespan is typically up to 10 years, rarely 15 years.[21][22][23]
Pronghorn herd, Yellowstone National Park
Herd of pronghorns
Doe with fawns about an hour old, near Fort Davis, Texas, 1947. Photo by Smithsonian zoologist Helmut Buechner
Juvenile fawn in New Mexico
At the turn of the 20th century, members of the wildlife conservation group Boone and Crockett Club had determined that the extinction of the pronghorn was likely. In a letter from George Bird Grinnell, Boone and Crockett Club chairman of the game preservation committee, to Walter L. Fisher, Secretary of the Interior, Grinnell stated, "The Club is much concerned about the fate of the pronghorn which appears to be everywhere rapidly diminishing." By the 1920s, hunting pressure had reduced the pronghorn population to about 13,000.[7] Boone and Crockett Club member Charles Alexander Sheldon, in a letter to fellow member Grinnell, wrote, "Personally, I think that the antelope are doomed, yet every attempt should be made to save them." Although the club had begun their efforts to save the pronghorn in 1910 by funding and restocking the Wichita Game Refuge in Oklahoma, the National Bison Range in Montana, and the Wind Cave National Park, in South Dakota, most of the efforts were doomed since experience demonstrated that after initial increases the pronghorns would die off because of the fenced enclosures. In 1927, Grinnell spearheaded efforts along with the help of T. Gilbert Pearson of Grinnell's National Audubon Society to create the Charles Alexander Sheldon Antelope Refuge in northern Nevada. About 2900 acres of land were jointly purchased by the two organizations and subsequently turned over to the Biological Survey as a pronghorn refuge. This donation was contingent upon the government's adding 30,000 acres of surrounding public lands. On June 20, 1929, United States President Herbert Hoover included the required public lands upon request of the Department of Agriculture and the Department of the Interior after learning that the Boone and Crockett Club and the National Audubon Society were underwriting the private land buyout. On January 26, 1931, Hoover signed the executive order for the refuge. On December 31, 1936, President Franklin Roosevelt signed an executive order creating a 222,000-hectare (549,000-acre) tract; this was the true beginning for pronghorn recovery in North America.[42]
The protection of habitat and hunting restrictions have allowed pronghorn numbers to recover to an estimated population between 500,000 and 1,000,000 since the 1930s.[2] Some recent decline has occurred in a few localized populations,[21] due to bluetongue disease which is spread from sheep, but the overall trend has been positive.
Pronghorn migration corridors are threatened by habitat fragmentation and the blocking of traditional routes. In a migration study conducted by Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society, at one point, the migration corridor bottlenecks to an area only 200 yards wide.[43]
Pronghorns are now quite numerous, and outnumbered people in Wyoming and parts of northern Colorado until just recently. They are legally hunted in western states for purposes of population control and food. No major range-wide threats exist, although localized declines are taking place, particularly to the Sonoran pronghorn, mainly as a result of livestock grazing, the construction of roads, fences, and other barriers that prevent access to historical habitat, illegal hunting, insufficient forage and water, and lack of recruitment.[2]
Three subspecies are considered endangered in all (A. a. sonoriensis, A. a. peninsularis), or part of their ranges (A. a. mexicana). The Sonoran pronghorn has an estimated population of fewer than 300 in the United States and 200–500 in Mexico, while there are approximately 200 Peninsula pronghorn in Baja California.[2] Populations of the Sonoran pronghorn in Arizona and Mexico are protected under the Endangered Species Act (since 1967), and a recovery plan for this subspecies has been prepared by U.S. Fish and Wildlife Service.[2] Mexican animals are listed on CITES Appendix I. Pronghorns have game-animal status in all of the western states of the United States, and permits are required to trap or hunt pronghorns.[2]
The pronghorn (UK: /ˈprɒŋhɔːrn/, US: /ˈprɔːŋ-/) (Antilocapra americana) is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American antelope, prong buck, pronghorn antelope and prairie antelope, because it closely resembles the antelopes of the Old World and fills a similar ecological niche due to parallel evolution. It is the only surviving member of the family Antilocapridae.
During the Pleistocene epoch, about 11 other antilocaprid species existed in North America. Three other genera (Capromeryx, Stockoceros and Tetrameryx) existed when humans entered North America but are now extinct.
As a member of the superfamily Giraffoidea, the pronghorn's closest living relatives are the giraffe and okapi. The Giraffoidea are in turn members of the infraorder Pecora, making pronghorns more distant relatives of the Cervidae (deer) and Bovidae (cattle, goats, sheep, antelopes, and gazelles), among others.
The pronghorn is the fastest land mammal in the Western Hemisphere, with running speeds of up to 88.5 km/h (55 mph). It is the symbol of the American Society of Mammalogists.
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